Ice-nucleating particle measurements from the M-Phase 2022 flight campaign

Ice-nucleating particle (INP) measurements were taken during the M-Phase flight campaign over the Labrador Sea in October-November 2022, including during cold air outbreaks (CAOs). Aerosol particles were collected onto polytetrafluoroethylene (PTFE) membrane filters with 1.2 µm pores (47 mm diameter, Sartorius) onboard the Facility for Airborne Atmospheric Measurements (FAAM) aircraft during flights. The filters were then analysed via droplet freezing assays performed directly on the PTFE filters, as per Price et al. (2018) and Raif et al. (2024): 2 µL droplets of purified water were pipetted in an array onto a PTFE filter atop a hydrophobic glass slide on an EF600 cyrocooler cold stage, then the temperature of the stage cooled at a rate of 1 °C/min to −40 °C, with the droplet freezing events recorded using a webcam. Handling blanks were taken throughout the campaign by inserting PTFE filters into the FAAM aircraft inlet system but not collecting any sample, then processing the filter as normal. Polycarbonate (PC) track-etched membrane filters with 0.4 µm pores (47 mm diameter, Whatman) were collected simultaneous to the PTFE filters for potential processing via different methods.